The present invention relates generally to medical devices and methods. More particularly, the present invention relates generally to methods, systems, and kits for perfusing and optionally cooling the cerebral vasculature of a patient with oxygenated blood or other media.
Cerebral ischemia, i.e., reduction or cessation of blood flow to the cerebral tissue, can be characterized as either focal or global. Focal cerebral ischemia refers to reduced perfusion to the cerebral tissue resulting from a partial or complete occlusion in the intracranial or extracranial cerebral arteries, e.g., stroke, subarachnoid hemorrhage spasms, iatrogenic vasospasm. Global cerebral ischemia refers to reduced perfusion to the cerebral tissue resulting from systemic circulatory failure caused by, e.g., cardiac arrest, shock, circulatory arrest, and septicemia.
Cardiac arrest is a major contributor to global cerebral ischemia. Cardiac arrest refers to cessation or significant reduction of a patient""s cardiac output and effective circulation to vital organs, most importantly the brain. Cardiac arrest can result from a number of causes, such as electrical dysfunction, mechanical failure, circulatory shock, or an abnormality in ventilation. Within minutes of blood flow cessation, tissue becomes ischemic (oxygen deprived), particularly in the heart and brain. Brain tissue is perhaps most immediately at risk, with severe, irreversible damage occurring minutes after the initial cardiac arrest. Patients in cardiac or circulatory arrest are usually treated by a combination of forced ventilation of the lungs and forced compression of the heart. Most commonly, cardiopulmonary resuscitation (CPR) is applied to the patient, with manual chest compression and mouth-to-mouth resuscitation. Advanced cardiac support (ACS) may also be provided in the form of drugs, defibrillation, and other techniques. Less commonly, open chest massage of the heart may be performed, particularly in a hospital setting where skilled surgeons may be present. Open chest heart massage is probably the most effective technique at resuscitating a patient and avoiding ischemic brain damage, but the technique is quite invasive and not available in most emergency situations.
CPR and other techniques which are directed at mechanical heart compression and lung ventilation do not usually provide adequate brain oxygenation. In addition, vasoconstrictors, e.g., epinephrine, administered during CPR are often either ineffective or given in dosages too high to produce systemic blood pressure required for cerebral perfusion. In the best cases, conventional cardiac resuscitation techniques will provide no more than 1 l/min of total blood circulation (with only about 200 ml/min passing through the cerebral vasculature) and no more than 5 to 15 mmHg of blood pressure. Normal circulation and blood pressure are 5 l/min and 80 to 100 mmHg, respectively, with about 1 l/min passing through the cerebral vasculature. Such flows are usually not adequate at normothermia. Even when CPR techniques are applied within the first several minutes of a cardiac arrest, the percentage of patients who survive without significant brain damage is very low. Significantly, most patients suffering from cardiac arrest die because of cerebral hypoperfusion.
Recognizing such problems, alternative techniques for treating patients in cardiac arrest have been proposed. Of particular interest to the present invention, the emergency use of cardiopulmonary bypass machines for supporting and cooling systemic circulation has been proposed. Generally, access is provided with a pair of catheters, where one of the catheters may be balloon-tipped to partition the circulation and permit the desired bypass. While such systems are theoretically effective, they do not isolate the cerebral vasculature and do not necessarily provide sufficient oxygenation of the brain. Moreover, the need to deploy intravascular catheters is time consuming and must be performed by a highly skilled and trained personnel.
Surgical procedures on the aorta are required for the treatment of a number of conditions, such as aortic aneurysms, occlusional diseases, aortic dissection, and the like. Exemplary procedures include conventional aortic aneurysm repair and grafting, endarterectomy for the treatment of aortic atheroma, stenting for the treatment of aortic atheroma or dissection, and the like. Such procedures frequently require that the aorta be surgically opened to permit reconstruction or other surgical modification. Surgically accessing and opening the aorta will usually further require that the patient""s circulation be arrested, i.e., blood flow through the aorta cannot be accommodated while the aorta is being surgically accessed. Cessation of systemic circulation places a patient at great risk, particularly in the cerebral vasculature where ischemia can rapidly lead to irreversible brain damage.
A number of techniques have been proposed to at least partially protect a patient having arrested circulation during a variety of aortic procedures. It will be appreciated that conventional cardiopulmonary bypass (CABG) techniques will generally not be useful when the aorta does not remain in tact. Thus, various alternative protective protocols have been proposed.
xe2x80x9cRetrograde aortic perfusion (RAP) can be used when a procedure is being performed on the aorta between the heart and the aortic arch. The aorta is clamped beneath the aortic arch and retrograde aortic perfusion established, typically via femoral access. Advantageously, such retrograde perfusion can continue throughout the procedure since the operative site within the aorta is isolated by the clamp. RAP, however, is disadvantageous in a number of respects. In particular, retrograde perfusion often results in significant cerebral embolization from dislodgment of atheromatous material in the descending aorta and aortic arch. Such risk, as well as the limited region of the aorta that can be operated on, makes RAP less than ideal. Moreover, RAP is not useful for procedures distal or proximal to the isolated region of the aorta and is useful only at the beginning of procedures performed within the isolated aortic regionxe2x80x9d.
Another approach for protecting the brain during aortic arch procedures is referred to as hypothermic circulatory arrest (HCA). HCA relies on inducing marked hypothermia in the entire body prior to stopping blood circulation altogether. Circulation remains stopped during the entire aortic procedure, thus placing the patient at significant risk of ischemia (despite the hypothermia). The patient is at further risk because the whole body has been cooled, thus increasing the duration of the surgery to accommodate the time needed to return to normal body temperature. HCA has also been associated with systemic coagulopathy (impaired coagulation) in a significant number of patients. Coagulopathy can require blood and plasma transfusion, both of which have been associated with the risk of viral infection. Aortic surgery performed with HCA has a very high morbidity, typically about 20%.
In order to retain some cerebral circulation during the time the aortic arch is accessed, HCA may be combined with retrograde cerebral venous perfusion (RCP). A catheter is placed in the superior vena cava and oxygenated blood introduced. Flow is established in a retrograde direction up the vena cava into the brachial and jugular veins. Unfortunately, very little of the oxygenated blood will reach the cerebral vessels for a number of reasons. For example, as much as 85% of the blood will enter the brachial veins and go to the arms with as little as 205 of the blood entering the brain. Moreover, the jugular venous valves may inhibit the blood from reaching the cerebral vessels. Blood that does reach the cerebral veins immediately flows outwardly through the extensive collateral circulation without perfusing the brain tissue. The amount of blood that returns to the aorta from the carotid arteries represents no more than about 5% of the total blood that is initially introduced to the superior vena cava. Additionally, as observed by the inventor herein, such retrograde perfusion results in a build up of the cerebral pressure that further inhibits any blood inflow. For these reasons, HCA, even when combined with RCP, falls far short of providing adequate protection for the patient during procedures performed on the aorta.
Another procedure for perfusing the brain during aortic procedures has recently been proposed. The procedure is referred to as selective antegrade cerebral perfusion (SCP) and relies on introducing a catheter through the aorta into a carotid artery in order to perfuse the cerebral vasculature. Introduction of the catheter can dislodge atheromatous material which will often be present at the take-off from the aorta and which may thus cause cerebral embolization. Furthermore, in order to prevent air from entering the cerebral vessels, the carotid artery and all other cerebral arteries must be externally clamped or snared, which can cause atheromatous embolization. While the procedure can more effectively maintain cerebral perfusion than HCP, alone or combined with RCP, the risk of both air and atheromatous embolization more than outweighs any associated benefits from enhanced perfusion.
It would therefore be desirable to provide improved methods and systems for perfusing the cerebral vasculature of a patient suffering from either focal or global cerebral ischemia with oxygenated blood or other media in patients. Such methods and systems should be suitable for rapid deployment, be capable of use outside of a hospital environment, and should be capable of being performed with less skilled personnel than comparable catheter-based systems. Preferably, such systems may be deployed via direct percutaneous cannulation of the patient vasculature. In addition, the method and systems of the present invention should be suitable for use with patients undergoing cardiac and vascular procedures where it is desirable to perfuse and/or isolate the cerebral vasculature. At least some of these objectives will be met by the invention of the present application.
For these reasons, it would be desirable to provide improved methods, systems, and kits for protecting the brain and cerebral vasculature during the performance of surgical procedures on the aorta. In particular, it would be desirable to provide for cerebral perfusion which is both antegrade and continuous throughout performance of the aortic procedure and which would enable profound cerebral hypothermia without systemic hypothermia. It would be further desirable to provide for improved isolation of the cerebral vasculature, still more preferably with minimum and ideally no external clamping. It would be still further desirable to minimize the risk of air and/or atheromatous embolization in the cerebral vasculature or elsewhere as a result of the aortic procedure. Such methods, systems, and kits should be compatible with reduced and/or localized hypothermia, particularly hypothermia directed specifically at the cerebral vasculature. In addition, cerebral isolation, perfusion and cooling should be compatible with systems and methods for perfusing non-cerebral portions of the patient""s vasculature. At least some of these objectives will be met by the invention described hereinafter.
Selective cerebral perfusion (SCP) procedures are described in Kazui et al. (1992) Ann. Thorac. Surg. 53:109-114; Mohri et al. (1993) Ann. Thorac. Surg. 56:1493-1496; and Tanaka et al. (1995) Ann. Thorac. Surg. 59:651-657. Advanced cardiac life support techniques are discussed and compared in Tucker et al. (1995) Clin. Cardiol. 18:497-504. Emergency cardiopulmonary bypass using access needles introduced via a cut-down procedure is described in Litzie, U.S. Pat. No. 4,540,399. Emergency cardiopulmonary bypass using catheter-based access is described in Safar et al., U.S. Pat. No. 5,383,854; Safar et al., U.S. Pat. No. 5,308,320; Buckberg et al., U.S. Pat. No. 5,011,469; and Safar (1993) Ann. Emerg. Med. 22:58/324-83/349. A cardiopulmonary bypass system with cooling having a balloon tipped cannula for accessing the inferior vena cava and an anastomotically attached catheter for accessing the femoral artery is described in Sausse, U.S. Pat. No. 3,881,483. Cerebral infusion with cooled and/or preservative media is described in Klatz et al., U.S. Pat. Nos. 5,149,321; 5,234,405; 5,395,314; 5,584,804; and 5,653,685. Aortic perfusion with balloon catheters is described in Paradis, U.S. Pat. No. 5,334,142; Manning, U.S. Pat. No. 5,437,633; and Manning et al. (1992) Ann. Emerg. Med. 21:28-35. Coronary and/or cerebral retroperfusion is described in Pizon et al., U.S. Pat. No. 4,459,977; Jackson, U.S. Pat. No. 4,850,969; Jackson, U.S. Pat. No. 4,917,667; and Grady, U.S. Pat. No. 5,084,011. Other relevant patents include Barkalow et al., U.S. Pat. No. 4,198,963; Ward et al., U.S. Pat. No. 5,531,776; and Meyer, III, U.S. Pat. No. 5,626,143.
According to the present invention, methods, systems, and kits are provided for perfusing an oxygenated medium, usually autologous blood, through the cerebral vasculature of patients suffering from global ischemia caused by, e.g., cardiac arrest, shock, circulatory arrest, and septicemia; focal ischemia caused by stroke, subarachnoid hemorrhage spasms, iatrogenic vasospasm; or, cerebral edema, e.g., head trauma. The method, systems, and kits are useful not only in providing selective isolated cerebral perfusion during all conditions of cerebral ischemia, but also in reducing the dosage of vasoconstrictors required to achieve a desired perfusion pressure.
Optionally, in addition to improving cerebral perfuision, the methods of the present invention may combine or otherwise rely on cooling of the patient""s head and cerebral vasculature in treatment of both global and focal cerebral ischemia to inhibit tissue damage resulting from lack or limitation of cerebral blood circulation. Usually, the oxygenated medium which is circulated as part of the methods of the present invention will be cooled in order to cool the brain tissue and reduce the risk of ischemic damage. Further optionally, the patient""s head may be cooled even prior to initiating perfusion of externally oxygenated, optionally cooled blood. In some instances, the cooled blood can be used to externally cool the patient""s head during the treatment protocol, e.g., by passing the blood through a helmet or other structure which permits the blood to selectively cool the head. This selective isolated cooling of the head and/or cerebral vasculature is desirable and preferred over systemic cooling, since coagulopathy, poor healing, cardiac arrhythmia and cardiac arrest can ensue as a result of systemic cooling.
The methods of the present invention for improving cerebral perfusion comprise accessing at least one extracranial vein, such as the internal jugular vein, the femoral vein, and/or the subelavian vein, and accessing at least one artery which feeds the cerebral vasculature through incisions on any extracranial artery, such as the common carotid artery, the internal carotid artery, the femoral artery, or the subclavian artery. In providing both selective isolated perfusion and cooling of the cerebral tissue, the methods comprise assessing at least one thing at location(s) which drain at least a portion of the cerebral vasculature, such as the internal jugular vein and/or external jugular vein, and assessing at least one artery which feeds the cerebral vasculature through incisions on any extracranial artery, such as the common carotid artery, the internal carotid artery, the femoral artery, or the subdlavian artery. In emergency cases, access will usually be provided by a percutaneous needle stick as described in more detail below. When performed in conjunction with aortic arch or other cardiac surgery, in contrast, the access will usually be provided via surgical exposure of the target vein(s) and artery(ies). An oxygenated medium is flowed from the arterial access location through the cerebral vasculature to the venous access location in order to perfuse the cerebral vasculature with the oxygenated medium. The vein(s) and artery(ies) are chosen to provide access to at least a major portion of the blood circulation through the cerebral vasculature. Preferably, the vein(s) and artery(ies) will also be directly accessible via a percutaneously inserted needle or other cannula for emergency performance of the procedures in the field. Suitable veins include the internal and/or external jugular vein, the superior vena cava, and the like. Suitable arteries include the common carotid arteries, the external and internal carotid artery, and the like. The particular access sites in each of the artery and vein will be selected based primarily on percutaneous accessibility. Preferred venous access sites lie within the internal jugular vein and preferred venous access sites lie within the common carotid artery.
After access is established, typically using percutaneously introduced needles, cannulas, or other conduits, a flow of oxygenated medium is initiated at a rate sufficient to provide oxygen to the brain tissue. The rate will depend on the amount of oxygen being carried by the oxygenated medium, typically being in the range from 0.1 l/min to 1.5 l/min, typically from 0.2 l/min to 1 l/min. For oxygenated autologous blood, the rate will typically be in the range from 0.2 l/min to 1 l/min. In some instances, in order to inhibit possible reperfusion injury, it will be desirable to initiate the flow rate of oxygenated medium at a relatively low rate and subsequently increase the flow rate to a final rate within the ranges set forth above. Usually, the final flow will be maintained at a steady rate, but it will also be possible to initiate a pulsatile or other nonsteady flow rate.
In order to enhance the efficiency of oxygenated medium delivered to the cerebral vasculature, it will usually be desirable to at least partly occlude the access blood vessel(s) near the access sites in order to prevent flow away from the cerebral vasculature. That is, at the venous access site(s), the vein will be occluded in order to inhibit flow caudal to the access location. At the arterial access site(s), the artery will be occluded to inhibit flow into the aorta. As described in more detail in connection with the systems of the present invention, such occlusion will typically be provided by inflatable occluding balloons on the access needles, cannulas, or other conduits.
In the preferred methods of the present invention, the oxygenated medium will consist essentially of blood, usually patient autologous blood, and the blood will be recirculated from the venous access location to the arterial access location using a pump. In addition to the primary antegrade flow, some flow may occur in a retrograde direction to the contralateral hemisphere and/or posterior territories as well. The blood will be extracorporeally oxygenated and optionally cooled, typically to a temperature in the range from 7xc2x0 C. to 35xc2x0 C. External pumping, oxygenation, and cooling can be provided by systems of a type used for cardiopulmonary bypass procedures.
Alternatively, the oxygenated medium may comprise a synthetic oxygen carrier, such as a perfluorocarbon, or other synthetic blood substitute material. In some instances, such synthetic oxygen carriers may be combined with patient or non-autologous blood. The synthetic oxygen carriers may be preoxygenated and flowed through the cerebral vasculature only once. In such cases, a large reservoir of the synthetic oxygen carrier may be provided, passed through the cerebral vasculature, and collected as it passes out of the venous access site. Alternatively, the synthetic oxygen medium, optionally combined with blood, may be extracorporally recirculated and oxygenated as described above for autologous blood.
In all cases, the oxygenated medium may have other biologically active agents combined therewith. For example, drugs and biological agents which inhibit deterioration of brain tissue in cases of limited oxygen supply may be utilized. Such compositions include NMDA receptor-inhibitors, calcium-channel blockers, anticoagulants, glutamate inhibitors, free-radical inhibitors, vasodilators, and the like.
The present invention still further provides improved methods for selective isolated cerebral perfusion in patients with global or focal ischemia. Such improved methods comprise isolating at least a portion of the patient""s cerebral vasculature from the remainder of patient circulation, typically by partitioning using occlusion balloons as described in more detail hereinafter. Patient blood is oxygenated and recirculated through the isolated vasculature in order to inhibit ischemia and resulting damage to brain tissue while steps are taken to treat the cardiac arrest.
In yet another aspect of the method of the present invention, improved antegrade cerebral perfusion with an oxygenated medium comprises introducing the oxygenated medium, typically autologous blood, to a carotid artery to establish antegrade flow into the cerebral vasculature. The oxygenated medium, after it has passed through the cerebral vasculature, is collected through a jugular vein. Such improved methods may be used with both once-through perfusion using a synthetic oxygen carrier and/or heterologous oxygenated blood. More usually, such improved methods will be used with extracorporeal recirculation and oxygenation of autologous blood.
Systems according to the present invention for recirculating and oxygenating blood in the cerebral vasculature of a patient comprise a venous cannula, an arterial cannula, a pump, and an oxygenator. The venous cannula typically has a lumen diameter in the range from 2 mm to 4 mm and includes a distal occlusion balloon, wherein the cannula and balloon are sized to access and occlude a vein which drains the cerebral vasculature, typically a jugular vein. The arterial cannula typically has a lumen diameter in the range from 2 mm to 4 mm and also has a distal occlusion balloon, and the cannula and balloon are sized to access and occlude an artery which feeds the cerebral vascular, typically the common carotid artery. The pump may be connected between the venous cannula and the arterial cannula to circulate blood from the venous cannula to the arterial cannula, typically at a flow rate in the ranges set forth above. The oxygenator processes the externally circulating blood to provide a desired degree of oxygenation, also within the ranges set forth above.
The present invention still further provides kits including a venous cannula sized to access a vein which drains the cerebral vasculature and an arterial cannula sized to access an artery which feeds the cerebral vasculature. Such kits will further include instructions for use according to any of the methods set forth above. Additionally, the kits may comprise a package for holding all or a portion of the kit components, typically in a sterile condition. Typical packages include trays, pouches, boxes, tubes, and the like. Preferably, the cannulas will each have an occlusion balloon sized to occlude the respective blood vessel lumen into which they are placed. Other optional kit components include oxygenated medium, drugs to be delivered via the flowing blood or other oxygenated medium, catheters for connecting the cannulas to an extracorporeal recirculation/oxygenation cooling system, cassettes for use with such extracorporeal recirculation systems, cooling elements, thermometers, pressure transducers, and the like.
In still other embodiments, methods, systems, and kits are provided for isolating and perfusing the cerebral vasculature, usually to facilitate access to a patient""s aorta, during performance of a diagnostic or interventional procedure on the aorta, more usually during performance of an open surgical interventional procedure on the aorta, such as repair of an aortic aneurysm, dissections, reconstruction of the aorta, endarterectomy, or the like. The heart will usually be arrested during open surgical procedures where the aorta is opened and procedure is performed within the lumen of the aorta. In some instances, however, the heart may remain beating while the procedure is performed intravascularly, i.e. through using catheters and other instruments introduced from the peripheral vasculature and into the aorta. The methods of the present invention will serve primarily to isolate the cerebral vasculature and prevent gaseous and atheromatous emboli from entering the cerebral vasculature while the vasculature is perfused with an oxygenated medium.
Methods according to the present invention comprise internally occluding blood flow to the arterial cerebral vasculature at a location(s) above the aortic arch. At a minimum, blood flow to the right cerebral vasculature will be internally occluded. Preferably, blood flow to both the right and left cerebral vasculature is internally occluded. Such internal occlusion is usually accomplished using an expansible occluder or partial occluder with central lumen, such as an inflatable balloon positioned at the distal end of a catheter, cannula, or other access device. The access device further provides for perfusion of an oxygenated medium into the occluded artery distal to the point of occlusion, e.g., the device may have a lumen that delivers the medium at a suitable positive pressure.
Occlusion of blood flow from the aortic arch and perfusion of oxygenated medium to the arterial cerebral vasculature may be accomplished in a number of ways, e.g., by occluding the right common carotid artery or by occluding an upstream portion of the brachiocephalic artery which-feeds the right carotid artery. In both cases, the oxygenated medium can be perfused distally of the balloon or other occluding device so that it flows up through the right common carotid artery into the cerebral vasculature. When occluding the brachiocephalic artery and perfusing the oxygenated medium upstream of the right common carotid artery, it may be desirable to at least partially inhibit blood flow through the right subdlavian artery, e.g. using another occluding balloon or using an externally applied tourniquet on the arm. Inhibiting the loss of oxygenated medium to the arm helps redirect the medium to the cerebral arterial vasculature through both the right common carotid artery as well as the right vertebral artery, assuming that the subdlavian artery is occluded at a point distal to the vertebral arterial branch. Other, more complex occlusion patterns could also be employed, although not necessarily being preferred.
Occlusion of blood flow from the aortic arch and perfusion of oxygenated medium to the left arterial cerebral vasculature may be effected within the left common carotid artery, the left subdlavian artery, and/or the left vertebral artery. When blood or other oxygenated medium is introduced into the left subdlavian artery, it may further be desirable to inhibit blood flow into the arm, e.g., by internally or externally occluding the left subdlavian artery at a point that prevents such blood flow.
In a presently preferred procedure, occluding balloons will be positioned within the brachiocephalic artery, the left common carotid artery, and the left subdlavian artery. Both the right subdlavian artery and the left subdlavian artery will be blocked, preferably with external tourniquets on the arms. Blood or other oxygenated medium will then be perfused into the arterial cerebral vasculature to points immediately upstream of each of the occluding balloons, preferably using lumens or other infusion components incorporated within the occluding devices themselves. Inhibition of blood flow down into the arms is beneficial since it redirects the blood or other oxygenated medium back into the cerebral arterial vasculature. While this approach may be optimal in many ways, the present invention can be carried out in other ways as well. Most simply, internal occlusion of the right brachiocephalic artery and perfusion of oxygenated medium distal to the point of occlusion may be sufficient in some cases by itself.
In many cases, it will be desirable to occlude the arteries at a point as close to the aortic arch as possible. In particular, this is true of the brachiocephalic artery, the left carotid artery, and the left subdlavian artery which branch directly from the aortic arch. Occlusion close to the aortic arch (i.e., immediately above the branch or within 3 cm thereof) is of benefit primarily because it enables the surgeon to access the artery and initiate the occlusion with minimal aortic dissection toward the neck. In other cases, of course, it will be possible to access any one of the brachiocephalic artery at a point close to the aortic arch and to intravascularly advance an occluding balloon or other devise to a desired point of occlusion. In some instances, it may even be desirable to deliver and position devices carrying multiple occluding balloons and/or lumens for delivering oxygenated medium to the cerebral arterial vasculature.
Access to the occlusion site and the target artery may be obtained in a variety of ways. For example, the target artery may be surgically exposed when the chest and neck are opened as part of a procedure being performed on the aortic arch. In such cases, small incisions can be made directly into the wall of the target artery to permit introduction of the occluder. Alternatively, in procedures that are performed away from the aortic arch and/or where it is not desired to surgically open the patient above the target sites within the arteries, the target sites can be accessed by conventional cut-down procedure or a needle-based procedure, such as the Seldinger technique. As yet another alternative, the arterial vasculature can be accessed at a LL point remote from the desired point of occlusion, e.g. in the femoral artery or in an artery of the arm, such as the axillary or brachial artery. The balloon or other occluding member on the catheter may then be intravascularly advanced from the access location to the desired point of occlusion in a conventional manner, e.g. over a guidewire under fluoroscopic observation. An approach to a desired occlusion point within the brachiocephalic artery and/or the right common carotid artery from an artery in the arm may be preferred since no catheter would be present in the aortic arch itself.
The oxygenated medium will usually be blood, more usually being autologous blood obtained from the patient being treated. In the most usual cases, patient blood will be recirculated through a conventional blood pump and oxygenator so that the patient may be continuously supplied with oxygen in the perfused cerebral vasculature. The blood or other oxygenated medium will also be cooled in order to induce selective hypothermia within the cerebral vasculature. A preferred hypothermic temperature for the brain will be in the range from 7xc2x0 C. to 35xc2x0 C., more preferably from 9xc2x0 C. to 30xc2x0 C. The actual temperature that is maintained will depend both on the temperature and the flow rate of the oxygenated medium, with higher flow rates generally requiring less cooling to achieve the target hypothermic temperature. Useful flow rates for the oxygenated medium will be in the range from 300 ml/minutes to 1500 ml/minutes, typically from 400 ml/minute to 1000 ml/minute without hypothermia, and from 80 ml/minute to 600 ml/minute, typically from 150 ml/minute to 400 ml/minute with hypothermia induced in the patient. Generally, the patient requires progressively less oxygen with increased hypothermia, allowing the flow rates of oxygenated cooled medium to be decreased. A sufficient flow of the oxygenated medium should be maintained, however, in order to maintain the desired level of hypothermia. Suitable temperatures will be in the range from 8xc2x0 C. to 35xc2x0 C., typically from 14xc2x0 C. to 30xc2x0 C. It will be appreciated, of course, that the values of temperature, flow rate, and degree of oxygenation will be quite interdependent in that particular optimum values might be selected for individual patients and/or for different procedures.
The methods of the present invention will-find their greatest use in open and thoracoscopic surgical procedures where the aorta is exposed and surgically opened to permit performance of the desired procedure. In such cases, the heart will be arrested and the perfusion of the oxygenated medium will be relied on to achieve adequate oxygenation of the brain tissue and to avoid deleterious ischemia. Generally, the flow rates and temperatures set forth above will be sufficient to both achieve adequate perfusion and avoid ischemia. After the open procedure is completed, and the aorta is surgically closed, heart function may be reestablished. In order to avoid the release of emboli from the aorta into the cerebral vasculature, occlusion of carotid artery(ies) will be maintained for a minimum amount of time after heart function has been reestablished, typically for at least about 2 minutes, preferably for at least about 5 minutes, in order to permit atheromatous debris and air to be cleared from the aorta and away from the brain.
Occlusion of the selected arteries with the expansible occluder may be achieved in a variety of ways. Usually, in open surgical procedures, the outside of the target artery(ies) will be surgically exposed, permitting surgical incisions through the arterial wall(s). The expansible occluder may then be introduced through the incision, expanded, and perfusion of oxygenated medium established through the occluder. Alternatively, the expandable occluders may be introduced percutaneously through the patient""s neck and to the selected artery(ies) using conventional access techniques, such as the Seldinger technique. The expansible occluders will typically but not necessarily include catheters, cannulas, or other devices that permit the perfusion of the oxygenated medium through the expansible member and into the carotid artery for perfusion of the cerebral vasculature. It will also be possible to utilize separate devices for occlusion and for the perfusion of oxygenated medium. Fore example, it would be possible to employ an external clamp on the target artery and to utilize a separate needle or other cannula for infusion the oxygenated medium upstream of the clamp. The use of clamps, however, is generally not preferred since they can cause the release of significant amounts of atheromatous debris when released. It would also be possible to employ separate occluder(s) and infusion needles/cannulas, where the points of occlusion and infusion of oxygenated medium could be close together or spaced-apart. Also, as mentioned above, it will be possible to employ devices with more than one occlusion balloons and/or more than one infusion lumens in order to occlude and/or infuse oxygenated medium to different points in the vasculature from a single incision site.
As an alternative to access at points in the arterial vasculature above the aortic arch, the occlusion and perfusion devices may be introduced intravascularly through sites remote from the aortic arch. Most commonly, intravascular catheters may be introduced by conventional techniques through the femoral arteries and advanced to the target cerebral arteries using conventional techniques. Such access routes, will necessarily involve passing the catheters through the aortic arch itself. Thus, in many instances, it will be undesirable to use such intravascular techniques since they will lie within the regions where the procedure is being performed. Intravascular access could also be achieved in a retrograde manner through the axillary and brachial arteries as discussed above.
While it will be possible to perfuse a cold, oxygenated medium without collecting and recycling the medium, it will usually be desirable to establish a continuous extracorporeal flow circuit for filtering, oxygenating, and returning patient blood or other oxygenated medium to the patient. The oxygenated medium perfused into the arterial cerebral vasculature will generally flow through the anterior and posterior regions of the brain and into the venous system of the brain. From the venous system, the oxygenated medium will flow outwardly from the brain, primarily from the jugular veins. Thus, it will be convenient to collect the oxygenated medium from the brain from at least one of the right and left internal jugular veins, preferably from both internal jugular veins, or from the superior vena cava into which the-jugular veins drain. This blood can then be returned to the extracorporeal blood pump, oxygenated, and cooled before return to the patient""s arterial cerebral vasculature. Additionally, a very small portion of the blood or other oxygenated medium perfused into the brain through the cerebral arteries may leak back into the aortic arch through the left vertebral artery if the left subdlavian artery is not occluded. This leakage, typically in an amount from 5 ml/minute to 25 ml/minute, can be suctioned or otherwise collected by the surgeon and returned to the extracorporeal circulation system.
The brain and cerebral vasculature are at greatest risk from embolization and ischemia during the performance of aortic procedures that require arresting of the heart. Other portions and tissues within the body, however, are also at significant risk and in some cases it may be desirable to establish a perfusion of oxygenated medium through the noncerebral vasculature, in particular the vasculature in the lower portion of the patient""s body. For example, oxygenated blood or other medium can be introduced into the aorta below the aortic arch, where the aortic arch is isolated using an expansible occluder or other conventional occlusion device. The oxygenated medium will thus flow to the lower portion of the patient""s body where it will collect in the venous system and be returned towards the patient""s heart through the inferior vena cava. By occluding the inferior vena cava, again typically using an expansible occluder, the blood or other oxygenated medium may be collected and returned to an extracorporeal oxygenation, pumping, and optional cooling circuit.
The present invention still further provides kits including one or more expansible occluders adapted to occlude selected artery(ies) as described above. Such kits will further include instructions for use according to any of the methods set forth above. Additionally, the kit may comprise a package for holding all or a portion of the kit components, typically in a sterile condition. Typical packages include trays, pouches, boxes, tubes, and the like. Preferably, the cannulas will each have an occlusion balloon sized to occlude the respective blood vessel lumen into which they are placed. Other optional kit components include oxygenated medium, drugs to be delivered via the flowing blood or other oxygenated medium, catheters for connecting the cannulas to an extracorporeal recirculation/oxygenation cooling system, cassettes for use with such extracorporeal recirculation systems, cooling elements, thermometers, pressure transducers, and the like.